1. Field of the Invention
The present invention relates to an apparatus and method for detecting a transmission mode in a digital audio receiver adopting an orthogonal frequency division multiplexing (OFDM) scheme for broadcasting, and more particularly, to an apparatus and method for detecting each transmission mode by detecting the starting and ending points of an OFDM signal. The present invention is based on Korean Patent Application No. 200-4731.
2. Description of the Related Art
Digital audio broadcasting systems (DAB) support four transmission modes, each of which is characterized according to the frequency band and broadcasting receiving region. The DAB transmits audio signals using an orthogonal frequency division multiplexing (OFDM) scheme. For the reception of audio signals, DAB receivers must detect first the mode of a transmission frame. U.S. Pat. No. 5,862,226, filed on 11 Feb. 1997 and issued to Stefano Cervini, discloses an automatic mode detection in digital audio receivers. FIG. 1 illustrates the configuration of the conventional mode detection apparatus. In the operation of the mode detection apparatus, as shown in FIG. 1, a Fast Fourier Transform (FIT) block 110 calculates the FFT on a received signal S(n) in parallel for each OFDM symbol length (for example, symbol lengths of 128, 256, 512, 1024 and 2048 samples). A division block 120 divides complex numbers output from the FFT block 110 by a corresponding OFDM symbol length. An inverse FFT (IFFT) block 130 executes the calculation of the IFFT on the signals output from the division block 120, according to a time decimation algorithm, of the type commonly referred to as “butterfly”. A magnitude calculation block 140 calculates the magnitude of the numerical sequences output from the IFFT block 130. A peak value detection block 150 detects the peak value among the outputs from the magnitude calculation block 140, and stores the respective peak value for each numerical sequence in an N number of registers. A discrimination block 160 calculates the square of the calculation results of the IFFT module, relative to the numerical sequences corresponding to the different numbers of samples, detecting the peaks of the different numerical sequences resulting from the preceding calculation of the square and accumulating the relative peak values in an N number of registers, for each of the sequences. A minimum value estimation block 170 chooses a minimum value among the maximum values calculated in the discrimination block 160 and stored in the registers, and determines the transmission mode.
In the conventional mode detection apparatus and method, an input signal S(n) is subjected to as many parallel time-to-frequency domain transformations as the different numbers of samples, so that the calculation processes are complicated and the processing speed is delayed. In addition, the use of the FFT block complicates the configuration of the system. The conventional mode detection apparatus and method need additional registers for temporarily storing the IFFT results prior to comparisons of the IFFT results for calculating the correlations of each mode.